The disclosed technology relates generally to methods and systems for applying tree search and recursive based algorithms for codebook searches, and more particularly to codebook searches in a closed-loop multiple-input multiple-output (MIMO) transmission or storage system.
With the continuing demand for higher-speed digital communications systems and higher-density digital storage systems, various techniques have been applied to increase the efficiency of these systems. For example, closed-loop MIMO precoding may greatly increase spectrum efficiency and improve receiving quality in such systems. These techniques are so effective, that they have been widely adopted in many wireless and communication standards. However, in some cases the increase in spectrum efficiency and receiving quality comes at a cost. In particular, the added step of searching for an “optimal” precoding parameter may deteriorate the performance of such systems; in some case the performance degradation may be quite substantial.
In many cases, the precoding may be implemented using codewords that are derived from predetermined codebooks, which may be defined by a particular standard for communication. These codebooks may range in the number of codeword entries as well as in the size of the entries themselves. In a communications or storage system, a particular codeword is chosen to precode data streams at a transmitter so that the data streams may be effectively received and used by a receiver. During the normal course of operation of the system, conditions may change in the communication channel such that the chosen codeword is no longer the best codeword to use for precoding.
In such a situation, it may become necessary to search the codebook for a codeword that may be better suited for precoding a data stream given the current channel conditions. Because of the size of many codebooks, this search may be quite time and resource intensive. Thus, it becomes difficult to effectively and efficiently search through a codebook for the best codeword.